For LTE-A (Long Term Evolution Advanced), to support system bandwidths wider than LTE (Long Term Evolution), for example 100 MHz, one possibility is to directly distribute a frequency spectrum with a bandwidth of 100M as shown in FIG. 1; the other possibility is to aggragate some spectra distributed to the present systems so as to form large bandwidths for long-term evolution multicarrier systems. Uplink and downlink carriers in the system can be arranged asymmetrically at this time, that is to say, a user will conduct downlink transmission through occupying N≧1 carriers and uplink transmission through occupying M≧1 carriers as shown in FIG. 2.
An LTE-A system can support 5 carriers at most to aggregate at present. An LTE-A user equipment (UE) needs to feed back the information on Acknowledgement (ACK)/Negative Acknowledgement (NACK) of a plurality of downlink carriers and downlink subframes in the same uplink subframe. In the LTE-A system, a transmission scheme of PUCCH (Physical Uplink Control Channel) Format 1b with channel selection can be adopted for ACK/NACK feedback information less than 4 bits. For a FDD (Frequency Division Duplex) system, the typical application scene of this scheme refers to the aggregation of 2 carriers.
PUCCH Format 1b with channel selection differentiates different statuses of ACK/NACK feedback information through selecting and transmitting a plurality of channel resources via UE. ACK/NAK mapping table is used to realize the mapping among ACK/NACK feedback information to be fed back, actual channel transmission information (namely 4 constellation points modulated by PUCCH format 1b QPSK), and transmission channels. For ACK/NACK feedback with 2, 3 and 4 bits, 2, 3 and 4 uplink control channel resources are required respectively.
In an LTE system, all channel resources used for ACK/NACK transmission through PUCCH Format 1b with channel selection refer to implicit channel resources. The implicit channel resources mean uplink control channel resources reserved in control information areas of a fixed downlink carrier corresponding to an uplink carrier. The minimum unit of the control information area is CCE (Control Channel Element). UE can acquire an available uplink control channel resource through a minimum CCE number of each downlink control signaling sent on the downlink carrier. Such uplink control channel resource is abbreviated to “implicit channel resources” or “dynamic channel resource”.
In an LTE-A system, implicit channel resources on each UL CC (Uplink Component Carrier) are reserved only for a PDCCH (Physical Downlink Control Channel) paired with a DL CC (Downlink Component Carrier), while the PUCCH can be sent only on a UL PCC (Uplink Primary Component Carrier). Thus for a UE equipment, implicit channel resources only exsit on a UL PCC. In consideration that the UL PCC reserves resources only for a DL PCC (Downlink Primary Component Carrier), implicit channel resources only exsit on the PDCCH sent on a DL PCC. Thus not all channel resources required for PUCCH format 1b with channel selection are acquired from implicit channel resources.
It is necessary to design new ACK/NACK mapping table in the LTE-A system to meet the following requirements:
(1) Try to use the implicit resources reserved on UL PCCs to reduce the consumption on uplink control channel resources;
(2) Be applicable to inter-carrier dispatching and non-inter-carrier dispatching simultaneously to reduce standard complexities;
(3) Avoid many-to-one state in an ACK/NACK mapping table in LTE system;
(4) Be capable of solving the ambiguities during DL CC reconfiguration or when data packet scheduling only exists on a DL PCC, that is to say, a rollback of the PUCCH format 1a/1b transmission method in LTE Rel-8 can be implemented when UE receives data packet transmission only on the DL PCC (preferably, a base station sends the downlink data of a subframe only on the DL PCC during DL CC reconfiguration; or UE configures a plurality of DL CCs, while the base station dispatches data packets of a subframe only on the DL PCC). Meanwhile, it is necessary to ensure that QPSK constellation points and channel resources used for ACK/NACK transmission through a PUCCH format 1b with channel selection scheme are consistent with QPSK modulation symbols (or named constellation points) and channel resources used by ACK/NACK corresponding to the transmission of a data packet on main carrier by PUCCH format 1a/1b.
When an LTE-A Rel-10 system supports the rollback of Rel-8 PUCCH format 1a/1b transmission, the inconformity of UE and eNB (evolved NodeB, namely a base station) on a transmission scheme actually adopted by the UE should be solved, which comprises:
Condition 1: When the effective time of an eNB is different from that of UE during DL CC reconfiguration, the inconformity of the eNB and UE on the configuration number of DL CCs may exist.
For example, when the number of CC reduces from two to one during DL CC configuration by UE, eNB dispatches one codeword on a DL PCC and expects to adopt PUCCH format 1a on the UL PCC (FDD system: transmission with single codeword or a plurality of codewords with one dispatched codeword; or TDD system: transmission with single codeword or a plurality of codewords with one dispatched codeword) to receive one-bit ACK/NACK feedback information or adopt PUCCH format 1b (FDD system: transmission with a plurality of codewords with two dispatched codewords; or TDD system: transmission with a plurality of codewords with two dispatched codewords) to receive two-bit ACK/NACK feedback information.
However, before taking into effect, UE will still work under 2DL CC configuration, generate ACK/NACK feedback bits according to 2CC configuration and adopt a PUCCH format 1b with channel selection scheme on a UL PCC to transmit ACK/NACK feedback information. If QPSK modulation symbols and transmission channels determined after channel selection by UE are inconsistent with PUCCH format 1a/1b, an eNB cannot receive ACK/NACK information correctly. On the contrary, when the number of CC increases from one to two during DL CC configuration by the UE, the inconformity mentioned above will still exsit.
Condition 2: When UE configures a plurality of DL CCs, while an eNB only dispatches on a DL PCC, the inconformity of eNB and the UE on the actual transmission scheme of the UE will exsit.
For example, when an eNB only dispatches the data packet transmission of a subframe on a DL PCC, the eNB expects to adopt PUCCH format 1a (single-codeword dispatching)/1b (multi-codeword dispatching) on the UL PCC to receive ACK/NACK feedback information.
However, UE configuration is conducted on two DL CCs. Thus regardless of the number of DL CC where UE receives data packets, UE will generate ACK/NACK feedback bits according to 2CC configuration and adopt a PUCCH format 1b with channel selection scheme to transmit ACK/NACK feedback information on a UL PCC. If QPSK modulation symbols and transmission channels determined after channel selection by the UE are inconsistent with PUCCH format 1a/1b, an eNB cannot receive ACK/NACK information correctly.
To solve the above problems, it is necessary to ensure that ACK/NACK mapping table design meets the condition that transmission channels and modulation symbols corresponding to ACK/NACK feedback status during downlink transmission of a subframe on a DL PCC should coincide with PUCCH format 1a/1b.
In the mapping table of 2-bit ACK/NACK of a FDD system as shown in Table 1, two channel resources are used to conduct channel selection and a rollback of PUCCH format 1b cannot be supported (that is to say, the selected channels may be inconsistent with PUCCH format 1b, for example, channel 2 is selected). While a rollback of PUCCH format 1a can be supported in 2 statuses with background colors (that is to say, QPSK symbols and the selected channels are consistent with PUCCH format 1a).
TABLE 1Mapping Table of 2-bit ACK/NACK Feedback InformationACK/NACKChannel 1Channel 2 feedback status(nPUCCH,0(1))(nPUCCH,1(1))DL PCCDL SCCRSDataRSDataAA1−1AN/DTX1−1N/DTXA1 1NN/DTX1 1
In the mapping table of 3-bit ACK/NACK of a FDD system as shown in Table 2, DL PCC of the parts with background colors refers to mapping methods in multi-codeword mode. At this time, a rollback of PUCCH format 1b can be supported in 4 statuses with background colors (that is to say, QPSK symbols and the selected channels are consistent with PUCCH format 1b), while a rollback of PUCCH format 1a cannot be supported (that is to say, QPSK symbols and the selected channels are inconsistent with PUCCH format 1a); DL PCC of bold parts refers to mapping methods in single-codeword mode. At this time, 2 bold statuses can support a rollback of PUCCH format 1a (that is to say, QPSK symbols and the selected channels are consistent with PUCCH format 1a).
TABLE 2Mapping Table of 3-bit ACK/NACK Feedback Information
In the mapping table of 4-bit ACK/NACK of a FDD system as shown in Table 3, DL PCC refers to mapping methods in multi-codeword mode. At this time, a rollback of PUCCH format 1b can be supported in 4 bold statuses (that is to say, QPSK symbols and the selected channels are consistent with PUCCH format 1b); while a rollback of PUCCH format 1a cannot be supported (that is to say, QPSK symbols and the selected channels are inconsistent with PUCCH format 1a).
TABLE 3Mapping Table of 4-bit ACK/NACK Feedback InformationACK/NACKChannel 1Channel 2Channel 3Channel 4feedback status(nPUCCH,0(1))(nPUCCH,1(1))(nPUCCH,2(1))(nPUCCH,4(1))DL PCCDL SCCRSDataRSDataRSDataRSData——A, ADTX1−1A, NDTX1 jN, ADTX1−jN, NDTX1 1——
Wherein, the character A in Table 1, 2 and 3 represents ACK, and the character N represents NACK.
The feedback information of a downlink carrier corresponding to UE includes ACK (correctly-received data packets), NACK (incorrectly-received data packets) and DTX (Discontinuous Transmission, namely lost or non-dispatched data packets).
At present, ACK/NACK feedback information bits fed back by UE is determined based on the configured downlink carriers and transmission modes of each downlink carrier in the LTE-A FDD system, that is to say, it is necessary for the UE to feed back ACK/NACK with
      ∑          i      =      1        N    ⁢            C      i        ·    N  bits on an uplink subframe, wherein Ci represents codeword number of each downlink carrier (C=1 during single-codeword transmission and C=2 during multi-codeword transmission), different transmission modes (namely codeword number) can be used for different downlink carriers), and N represents the number of downlink carriers configured by the UE.
For a FDD system, when the multi-codeword transmission mode is used for a DL CC, namely MIMO (Multiple-Input Multiple-Out-put) transmission mode, it is necessary for UE to separately generate ACK/NACK feedback information with 1 bit no matter 2-codeword dispatching exsits on the DL CC actually. For the DL CC with only one-codeword transmission in MIMO transmission mode, it is necessary for the UE to generate a supposed ACK/NACK feedback status for the second codeword so as to meet the total number as
      ∑          i      =      1        N    ⁢      C    i  of ACK/NACK bits fed back by the UE. In LTE Rel-8 system, the UE generates NACK information for non-dispatched data packets/codeword positions.
During implementation of the embodiments of the present invention, the applicant finds that the following problems at least exist in the prior art:
In LTE-A Rel-10 system, when MIMO transmission mode is configured on PCC for UE, while one-codeword dispatching only exists on a DL PCC actually, a rollback of PUCCH format 1a should be supported to conduct 1-bit ACK/NACK transmission. In PUCCH format 1a, an ACK feedback status corresponds to the modulation symbol “−1”, and a NACK feedback status corresponds to the modulation symbol “1”. If NACK information is generated in the non-dispatched codeword position in accordance with LTE Rel-8 mode, the corresponding transmission symbol refers to “j” as shown in Table 1 and 2 rather than “−1” corresponding to PUCCH format 1a when the UE receives a codeword only on a DL PCC and ACK/NACK feedback information corresponding to the DL PCC generated by the UE refers to [A,N]. Therefore, a rollback of PUCCH format 1a cannot be realized.
At present, there are no corresponding solutions in the prior art.